In wireless communication devices, such as those commonly referred to as mobile stations (MSs), the SINR measurement is commonly used in a modulator/demodulator or modem when processing received data. In a code division multiple access (CDMA) system, the SINR, also defined as Eb/Nt (bit energy to noise power ratio), is a required measurement for the MS to support a fast Forward Power Control (FPC) algorithm. The fast FPC is intended to be deployed on the forward link of a third generation CDMA system as a means to increase the forward link capacity by providing more stringent control over the transmitted power of the base station (BS). The basic idea of the FPC algorithm is that the MS determines whether a serving BS should increase or decrease the transmitted power according to its received “instantaneous” SINR, as determined by current radio channel fading conditions. Specifically, the MS requests an increase in transmitter power when it experiences a deep fading condition (low SINR), and it requests a decrease in transmitter power when it experiences good channel conditions (high SINR).
For a single antenna receiver, the MS algorithm for SINR estimation is typically implemented as follows. First, the signal power (Eb) is computed by squaring the coherently combined amplitudes of the power control bits (FCH) or of the traffic symbols (SCH). This coherent summation involves the active fingers (whether assigned to a multipath or to another BS path in soft hand-off). here each finger is essentially a pseudo-noise (PN) and Walsh spreading code demodulator or correlator). The total noise power is, however, computed by adding the noise power levels estimated independently for each finger, and assuming these noise terms to be uncorrelated. In the case of multiple receiver antennas, however, the inventors have realized that the interference from a dominant neighbor BS (inter-cell interference) and/or the multipath interference (intra-cell interference) typically exhibits some degree of correlation across the antennas (spatial correlation) and, therefore, the underlying assumption of independent noise terms leads to an incorrect SINR estimation. Moreover, when an Optimal Combining (O.C.) scheme based on Minimum Mean Square Error (MMSE) criteria is used at the receiver, it is reasonable to assume that that the residual interference level observed at the O.C. output would differ from the sum of the interference power levels measured on each antenna branch, as the O.C. tends to suppress the correlated interference.